This invention relates to a camera in which a lens unit having a taking lens is made movable and the lens unit is made movable in the direction of the optical axis of the taking lens by a lens driving means.
As for the lens moving mechanisms of miniature-sized cameras, a helicoid-screw type mechanism has so far been most popularly used. In recent years, however, such helicoid-screw type mechanisms are getting difficult to use, because many complicated mechanisms provided around a lens unit require their own spaces and the cost reduction in camera manufacture is hardly to be made.
Particularly in a variable-focussing type camera in which a focal length is varied by moving the lens unit thereof in the direction of the optical axis of the lens unit, such a helicoid-screw cannot be used because of the spaces needed for moving the lens extensively to vary the focal length.
In the so-called retractable lens barrel type cameras which are to be used in the state that the movable lens unit thereof containing a taking lens system is pulled out to a prescribed position, it is substantially essential that the optical axis of the taking lens system is to be maintained vertically to a film plane when the lens unit is pulled out.
Particularly in a double-focus type camera of such a type that the focal length of the taking lens system is switched over to a long focal length when the lens unit is pulled out and to a short focal length when it is retracted by utilizing the above-mentioned retracting function, it is required to stop the movable lens unit in the state that the optical axis of the lens unit is vertical to a film plane when the movable lens unit is pulled out as well as it is retracted.
In the meantime, the above-mentioned movable lens unit is constructed to be a lens barrel of cylindrical shape. Therefore, the lens driving means is arranged to the outside of the circumferential surface of the movable lens unit and is connected to only a position of the circumferential surface of the lens barrel so as to drive the movable lens unit. Resultantly, the movable lens unit receives an unbalanced force, so that the constantly balanced posture thereof with the camera body can hardly be maintained.
To be more concrete, there is a clearance between the lens barrel and the section of inserting the lens barrel to move the lens barrel, and an unbalanced force is applied to the lens barrel by a driving force to be given onto only a position on the circumferential surface of the lens barrel. It will, therefore, result not only to cause a rough operation but also to be unable to keep the optical axis vertical to a film plane in the position of stopping the lens barrel.
In particular, with the advance of wider apertures of taking lens systems and hign-performance built-in shutter mechanisms, the outside diameters of lens barrels are getting large. Accordingly, the above-mentioned phenomena become more remarkable, and the influence thereof on the performance of cameras cannot be disregarded.
To avoid the above-mentioned troubles, the lens mount cannot help coupling to the lens with some clearance between them, and resultantly the direction of the optical axis of the lens is not fixed in a stable state but is constantly in a slightly instable state, and there is a fear that light is leaked from the section coupling to the lens mount. It is, therefore, required to take some countermeasure to avoid the above-mentioned troubles.